I should have known oscilloscopes don't measure current

[saturated]

I used to wonder how they measured current when set 📐 up in x-y mode

So I just accepted it 

So now I think they are just showing voltage. (Ya think ?!?!?  )

And yeah isn't that what oscilloscopes do 

I don't know the complete details I think the volts per division is set to "make it right" I'll see how it's done when I actually do this.  (Eek  )

So what's all the fuss about well in my book 📖 I'm working through the have a sections where students use a Tektronix 575.  I would love to have one but I looked at some and they are big and heavy, have lots of tubes (huh?!?) and $$$$ 

Dont get me wrong I would love to have one 

Now credit to the book 📚 they have instructions how to monitor Ic on the scope which is cool.

Seems like I saw on MEF one of the members here posted some beautiful pics of output characteristic curves 

[J M Fahey]

But you can!
It just needs the proper probe/adapter.
Everyday I measure power transistor current for servicing, power supply current under load, say when playing Music, current through a speaker, etc.
In this case,all it takes is a 0.1 ohm resistor in series with load, and clipping scope leads across it.
It turns 10A peak current into very measurable 1V peak, easy to display on any scope screen.

Warning: you need to have scope ground floating OR to have that resistor with one end grounded.

[saturated]

Yes sir thank you

I did make that mistake early on and had to learn the hard way 

I would put the scope lead and ground across a resistor like a volt meter   

It took me a while to figure out the scope lead ground was ground.

 

[saturated]

Been slugging it out 

Head is spinning 

Tried to do this experiment and my curve is backwards 

I did notice if I varied VBB it went up and down

VBB at about zero
I guess this is zero Ib (and or zero Ic)
You cannot view this attachment.

Then some Ib and or Ic
You cannot view this attachment.

Then more Ib and or Ic
You cannot view this attachment.

I tried flipping stuff around to no avail

Only when I put the scope on "inverse" did it look like I wanted

I'm disgusted but progress is progress

[saturated]

"schematic"

You cannot view this attachment.

 

[J M Fahey]

You made no mistake and its working as it should.

Only "problem" is that you are omitting a small fact:

A single transistor stage as shown is an *inverting* gain stage, so the higher the Vbb (or Vbe) the lower the Collector voltage (Vce).

Scope "does not lie" and shows it as it is.

[saturated]

Yes sir
I had to get out of bed and turn the lights on to further this quandary 

So look at this picture pretty sure at this time VBB was 1.6 v
You cannot view this attachment.

Some calculations below

You cannot view this attachment.

So I'm thinking that what I was seeing moving up and down while adjusting the variable resistor (VBB) was the collector current Ic

Problem is the resistor is nowhere near the collector and the whole rectified AC is really making things worse   

Yes sir thanks so much !!!    

[saturated]

I went back and played with this some more

With VBB at 3.6v Ib should be about 30 ua

Looking at the scope the collector current is showing five division at 0.1v setting so 5x 0.1 divided by 100 ohm should be about five milliamps
You cannot view this attachment.

If I change volts per division to 0.5 I get the same thing so that's cool
You cannot view this attachment.

The problem is if I use my meter to measure the voltage drop across the resistor I only get about half what I want (0.244 dc and 0.288 ac) 

You cannot view this attachment.

You cannot view this attachment.

Next I figured ok I can measure the collector current manually and then I only got 2.83 milliamps 

You cannot view this attachment.


Summary....idk why my meter is showing about half of what my scope is

Maybe it's got something to do with that diode 


Might be time to read up on half wave voltage and rms etc 

[saturated]

At least my evening tonight is already planned 

I'm going to run some low voltage ⚡ alternating current through a diode and compare measurements with the meter and scope.

[saturated]

Also I guess the one volt division for the horizontal is for VCE

You cannot view this attachment.

Because when I changed the volts per division the line got longer and shorter

 

[g1]

Might be time to read up on half wave voltage and rms etc 

Yes.  If there is any AC involved, meter can only give you RMS value.  Scope will not display RMS (except as calculated numeric readout on newer scopes).

[saturated]

After work I hooked up a simple circuit and checked it out

You cannot view this attachment.

Input was 10v and everything jived 

Next I made the same measurements between the series resistor and diode

The scope showed I lost half of my voltage which I presume makes sense but if I do the math on the rms meter reading I come up a little short I don't get 5 I get about 4.64 Vpp

So maybe I should account for voltage drop across the diode like the meter caught it but the scope did not....idk maybe the scope did catch it and I wasnt precise enough reading graticules

 

Also I was like oh hey the analog meter on my ugly variac must be rms 

You cannot view this attachment.

But alas I learned a bit more about X+Y mode it's just volts sideways and volts up and down.

 

[Tassieviking]

X and Y will show you the voltage one way and a time scale the other way, you have to change the time scale if you measure 50Hz and then change to a 5000Hz signal
Nearly all will show volts up and down and time scale left to right.

I think you are learning things faster then I am forgetting things, 5 years from now I will be asking you for help.